The present invention relates to a multipartite rock bolt to be used for consolidating rocks in general, and more particularly to a rock bolt for use in floor rock of underground excavations, particularly mines.
It is well known that, particularly in underground excavations, but also under different circumstances, a rock formation may have a tendency to disintegrate at a location where it is desired that it remain intact. So, for instance, in an underground mine, the mine floor, to give an example, may become unstable due to the pressure acting on the floor rock from the surrounding strata and, if unchecked, the floor rock would develop cracks and possibly move upwardly, thus creating problems and possibly hazardous conditions in the mine. This, of course, is very disadvantageous.
When it was in the past desired to consolidate rocks, that is, to prevent their undesired disintegration, resort has been had, in one of the conventional approaches, to the use of one-piece rock bolts usually made of steel which are introduced into and anchored, especially cemented, in respective holes drilled or otherwise provided in the rock formation to be prevented from disintegration. While these conventional one-piece rock bolts may be very advantageous in many applications, the possibilities of their use in underground excavations, particularly mines, are quite limited. More particularly, experience has shown that, for instance, if floor rock of an underground mine is to be consolidated, the desired or even necessary length of the rock bolt which is needed for reliably consolidating the floor rock, in most instances, is greater than the available height of the drift, adit, mining gallery or the like wherein the rock bolt is to be used for consolidating the floor rock. A further disadvantage of this prior-art approach is that, even if the one-piece rock bolts were originally long enough to be able to hold the floor rock in place, they do not give an assurance that the floor rock which is consolidated or stabilized in this manner will also withstand the subsequent enlargement of the mining gallery or the like. Thus, when this method is resorted to, it must be borne in mind that the floor rock which is secured in this manner is likely to break up and rise only at a later time than an unsecured floor rock, but that the process, more likely than not, will not be avoided altogether. In addition thereto, the steel rock bolts considerably hinder the subsequent removal of remaining coal from the floor of the underground mine by suitable machinery, such as lowerable loaders or the like. Thus, only a partial success has been achieved in stabilizing the floors of underground excavations, particularly mines, by resorting to the use of the one-piece anchor bolts, particularly inasmuch as the length of the one-piece elongated rock bolts is in most instances, as established by experience, insufficient.
In addition to the use of one-piece steel rock bolts, there has also already been proposed a different approach which resides in the use of two-piece rock bolts which incorporate separate elements which are connected to one another by means of external sleeves. Even this arrangement, however, is disadvantageous in some respects, particularly in view of the substantial cost of this combined arrangement, particularly the manufacturing cost of the connecting sleeves. Furthermore, the establishing of the connection between the individual elements is rather cumbersome. Another disadvantage of this approach is encountered when the rock bolt is to be cemented in the associated hole by a cementing material which is accommodated in cartridges which are to be penetrated by the rock bolt during the introduction thereof into the respective anchoring hole. Under these circumstances, the external sleeves connecting the individual elements of the rock bolt constitute a formidable hindrance to the introduction of the rock bolt into the associated anchoring hole.